Whichever model you have used as long as you extracted and made analysis from the case and explain the rationale/ valid points for the same, you will be collecting marks.
In P3, there may not be a standard answer for the case studies. You will be assessed on your analysis skills and how you have made use of information provided and derived any conclusion along with plausible assumption.
I guess thats the main criteria the examiner would be assessing us with.